The present invention relates to a magnetic eddy-current braking apparatus for assisting a frictional brake of a vehicle, and more particularly, to an eddy-current braking apparatus provided with a tube for protecting permanent magnets.
In a conventional eddy-current braking system provided with one or more magnet support tubes, relatively thick (approximately 10 to 16 mm) ferromagnetic plates have been used with a tube formed of a nonmagnetic material in order to prevent leakage of magnetic flux from permanent magnets. To accomplish the above, a magnetic plate is cast into a tube body formed of aluminum, or a tube is formed by a deformation process from stainless steel plate as a nonmagnetic material and ferromagnetic pole pieces are fitted into a number of openings provided in the tube and connected by welding. In the former method, manufacturing is difficult, and the yield or available percentage of aluminum cast product as a tube is poor. Further, according to the former method, the connecting strength between the magnetic pole pieces and the aluminum body of the tube is so weak that impregnating material or the like is filled into the clearances. Further, the manufacturing cost increases because of machining tolerances, when the outer peripheral surface of the tube opposite to the inner peripheral surface of the brake drum and the inner peripheral surface opposite to the magnets are subjected to required machining. Also in the latter method, it is difficult to reduce the cost of manufacturing because of costs associated with welding the magnetic plates to the tube.
In view of the aforementioned problems, the object of the present invention is to provide an eddy-current deceleration apparatus which is easier and less expensive to manufacture.